1. Field of the Invention
The present invention relates to an apparatus and method for the drawing of an optical fiber from a solid preform and more particularly, to a method wherein the fiber is drawn vertically.
2. Description of the Prior Art
A process of the above-mentioned type has been known for a long time (EP-PS 0 079 186), in which the cooling of the fiber drawn from the preform is carried out by means of a helium gas stream, which is blown diagonally against the fiber at the end of a cooling tube. The flow of the cooling gas, which is essentially laminar after contact with the fiber, as shown by experiments, does not permit an optimal cooling within the shortest time, so that the manufacturing or drawing rates using such a cooling process are limited. In addition to this, the gas stream directed diagonally against the fiber surface can be the cause of vibrations of the fibers, which have a disadvantageous effect on the quality of the fiber itself, and also on subsequent coating processes. As a result of the deficient cooling capacity of the gas in the known process, an increase in the drawing rate additionally leads to a considerable increase in gas consumption.
Although a process for the cooling of an optical fiber is known (EP-PS 174 699), by means of which the known vibrations are to be prevented, fiber cooling in this case nevertheless takes place essentially by transfer of heat to a cooling wall, with the heat transport medium consisting of a gas that is introduced into a space outside the actual cooling tube.